The present invention relates generally to commercial and institutional kitchen exhaust systems and, more particularly, to a device for controlling the exhaust fan above a burner, griddle or fryer. The cooking process of grilling or frying food generates substantial amounts of heat and cooking by-products such as grease particles, smoke and odors. In order to comply with local municipal codes as well as assuring health, safety, and cleanliness of the kitchen facilities, the heated and contaminated air is conventionally removed through an exhaust ventilation system. In a commercial cooking establishment, the exhaust ventilation system generally includes a vented hood extending over the area in which the food is grilled or fried and an exhaust fan motor for drawing the smoke and the like from the vented hood and up through the ventilation ducting to the exterior of the building.
Conventional exhaust systems draw a considerable quantity of air from the interior of the building along with the unwanted cooking odors and smoke. As a result, the air heated or cooled by the air conditioning system of the building is also exhausted to the outside, causing the thermostat of the air conditioner to run the air conditioner to replace the exhausted air. The resultant inefficient operation of the air conditioning system creates an added expense of operation for the owner of the building through higher utility bills, and it wastes valuable energy.
Numerous attempts have been made in the past to overcome the problems associated with exhaust ventilation systems. One approach has been to install a fresh air blower with an exhaust vent located near the cooking station, so that a quantity of outside air is blown into the cooking area to be exhausted along with the cooking by-products, thereby reducing the amount of air conditioning air exhausted. Such a system has proven unsatisfactory in periods of extreme hot or cold outside temperatures, since the introduction of such air into the interior of the building offsets the air conditioning system, causing it to run more often and consume more energy.
Other systems have been developed for automatically operating a cooking area ventilation system in response to detecting cooking by-products emitted from the cooking area, such as U.S. Pat. Nos. 4,121,199 and 3,690,245. Another system is controlled automatically by the presence of a cook at a cooking station. However, such prior devices are not entirely adequate to overcome the problem, since they often involve complicated and expensive circuitry and detection devices, mounted in the exhaust vents or in a floor mat adjacent the cooking area and are susceptible to damage from grease fires and spills which can occur in a cooking area.
It is seen then that a need exists for an exhaust ventilation system wherein the exhaust requirements are matched to the cooking load.